This author wanted to begin her 10-grade biology course with an authentic inquiry that included a review of equipment use, investigation methods, and critical thinking skills. She also wanted to engage students in the practice of science while teaching biological core ideas and crosscutting concepts. She was at a loss as to what that inquiry might be until she attended a National Science Foundation institute at Washington University in St. Louis. The lab, based on research by Brad Oberle and Barbara Schaal (2011), examines characteristics of tree leaves to determine their ecological performance. It is an example of "ecophysiology," the study of the adaptation of organisms' physiology to environmental conditions. Along with one of her colleagues, she modified the lab to introduce students to basic biological and ecological concepts. The inquiry includes a review of scientific practices; the use of measuring tools and proper units; the correct use of a microscope; and data collection, analysis, and presentation. It also meets several of the "Next Generation Science Standards" and can be adapted for different learning levels. This article describes the leaf investigation and how to modify it for any classroom.